The present invention relates to a cyclic refresh scheme for refreshing the charge or electrical signal, which has been lost due to leakage, stored on an array of dynamic memory cells.
A common approach to refreshing the charge, which has been diminished as a result of leakage through transistors, stored in a dynamic memory cell has been to interrupt the normal processor machine cycles every preselected number of cycles and to recharge the cells one row at a time. In the case of dynamic rams such refreshing of the stored charge must occur within an interval or a maximum time of about 100 microseconds to avoid excessive loss of charge. If, for example, one wishes to refresh every 16 machine cycles and an average frequency of 2 MHz is used for the processor machine, then for even a modest number of rows such as 128, the time between refresh is about 1 millisecond. Moreover, even if the latter time were acceptable, which it is not, the system deadtime introduced in order to carry out the refresh operation is not desirable.
Accordingly, it is an object of the present invention to provide an improved method of refreshing the stored charge on a dynamic memory cell. It is a further object of the invention to provide a method of refreshing the stored charge on a dynamic memory cell which does not interrupt the normal machine operation.